Photocatalytic Reduction Of CO₂ By Polypyridine Binuclear Iron And Manganese Complexes

For the carbon dioxide,to some extent,also a kind of potential carbon source,developing an efficient,highly selective and stable photocatalyst for reduction of carbon dioxide to fuel and valuable chemical products presents a huge challenge.Therein,transition metal complexes photocatalytic reduction of carbon dioxide has been a hot research field.In this paper,two kinds of dinuclear iron complexes F1 and F2 and four kinds of mononuclear manganese complexes M1,M2,M3,M4 were synthesized using L1,L2,L3 and L4 pyridine as ligand respectively.The photocatalytic properties of these six complexes were studied,and spectral analysis,electrochemical properties were also investigated.Specific results are as follows:1.Crystal data analysis of the complexes F2,M1 and M2 shows that F2 is a novel dinuclear iron complex,which is a special seven coordination compound.While M1 and M2 have been synthesized before,however,none of them has been studied on their photocatalytic properties of reduction carbon dioxide.2.In the process of photocatalytic reduction of carbon dioxide to carbon monoxide with iron dinuclear complexes F1,F2.The optimal photocatalytic activity of iron complexes was obtained by screening the light source,assembly method,solvent,photosensitizer,sacrificial agent and solvent ratio.The optimal conditions were as follows:blue LED light as irradiate source,DMF:TEOA=4:1（V:V）,photosensitizer[Ru（bpy）₃]²⁺was 0.045 mM,catalyst concentration was 0.1μM,and sacrificial agent BIH concentration was 0.059 M.Under this optimal conditions F1,F2 have better catalytic activity and the main product of photocatalytic reduction of CO₂ is CO,the by-product is H₂ mainly.TON_COO up to 52815 and 53128,respectively,the selectivity were 95.9%,96.8%.This is the first time that a synthetic iron binuclear complex was applied to system which photocatalytic carbon dioxide functionally.3.In the process of photocatalytic reduction of carbon dioxide to carbon monoxide with manganese complexes M1,M2,M3 and M4.The optimal reaction conditions were obtained through the photocatalytic reaction conditions:LED blue light irradiation,CH₃CN:TEOA=7:1（V:V）.The catalyst concentration was 0.1 mM,the photosensitizer[Ru（bpy）₃]²⁺concentration was 0.45 mM and the sacrificial agent BIH concentration was 0.052 M.Under the optimal conditions,the catalytic activity of M4 was the best,TON_COO reached 1038,followed by M2 and TON_COO reached 717,while the effects of M3 and M1 were poor with TON_COO of 167 and 99 respectively.At the same time,it was found that manganese complex also had some catalytic effect when using propylene carbonate as solvent.The conversion numbers of TON_COO corresponding to M1-M4 were 58,254,40,and 469 respectively.This shows that the catalysts with electron donating groups have a better catalytic effect.In addition,through the electrochemical research and theoretical calculations,discussion on mechanism was carried out.